This invention pertains generally to rotary seals and particularly to a seal adapted to provide a surface-to-surface seal between a shaft and a sleeve under static conditions yet allow relative rotation of the shaft and the sleeve with no surface-to-surface wear of the seal.
An important exemplary need for such seals is found in centrifugal filters as exemplified in U.S. Pat. No. 3,662,894. In such filters, as shown and described in said patent, a shaft carring a number of filter plates is stationary under static conditions, while a suspension of a liquid and often abrasive solids are being filtered through the plates. At selected times, but after the liquid has been drained under conventional practice, the shaft is rotated, often at high rotational speed, to throw accumulated solids radially outwardly from the plates by centrifugal force, thereby to clean the plates and allow the solids to be removed from the filter.
In such filters, particularly when the solids have been abrasive, rotary seals at the shafts have worn rapidly and eccessively, so as to allow consequent leakage of the materials being filtered. In prior designs, synthetic rubber lip seals or polytetrafluoroethylene-coated springloaded sealing rings, which have a generally U-shaped cross-section, were employed with only partially successful results.
Air pressure has been applied in an effort to flex such spring-load sealing rings to eliminate frictional wear of the seals as the shaft, against which such seals bear under static conditions, is rotated. These practices have proved partially successful, insofar as such seals have exhibited relatively longer useful lives; nonetheless, rapid uneven frictional wear of the seals and consequent leakage of the materials being filtered have often occured. Consequently, such filters have not often, if ever, been used in nuclear waste recovery applications and other applications were essentially no leakage can be tolerated.